The x‐ray light valve: A potentially low‐cost, digital radiographic imaging system‐concept and implementation considerations

Abstract

New x-ray radiographic systems based on large-area flat-panel technology have revolutionized our capability to produce digital x-ray images. However, these imagers are extraordinarily expensive compared to the systems they are replacing. Hence, there is a need for a low-cost digital imaging system for general applications in radiology. A novel potentially low-cost radiographic imaging system based on established technologies is proposed-the X-Ray Light Valve (XLV). This is a potentially high-quality digital x-ray detector made of a photoconducting layer and a liquid-crystal cell, physically coupled in a sandwich structure. Upon exposure to x rays, charge is collected on the surface of the photoconductor. This causes a change in the optical properties of the liquid-crystal cell and a visible image is generated. Subsequently, it is digitized by a scanned optical imager. The image formation is based on controlled modulation of light from an external source. The operation and practical implementation of the XLV system are described. The potential performance of the complete system and issues related to sensitivity, spatial resolution, noise, and speed are discussed. The feasibility of clinical use of an XLV device based on amorphous selenium (a-Se) as the photoconductor and a reflective electrically controlled birefringence cell is analyzed. The results of our analysis indicate that the XLV can potentially be adapted to a wide variety of radiographic tasks.

Low‐cost flexible thin‐film detector for medical dosimetry applications

“…In an attempt to minimize the use of expensive semiconductor material in these devices, and thus reduce costs, thin‐film structures have been developed and are available as commercial products from several companies such as PowerFilmSolar (Ames, IA) and Nanosolar (San Jose, CA). There are several approaches to photovoltaic technology: 10 , 11 , 12 , 13 , 14 , 15 , 16 thin‐film amorphous silicon (a‐Si) cells, organic photovoltaics (OPV), cadmium telluride cells (CdTe), or copper indium gallium selenide cells (CIGS). Compared to the conventional solid state detectors, thin‐film photovoltaics are thin, flexible, and adjustable to any shape or size and, in this respect, are similar to radiographic films.…”

The x‐ray light valve: A low‐cost, digital radiographic imaging system—Spatial resolution

“…Charge created in the bulk material, in this case a-Se, is guided by the electric field to form a charge image on the a-Se surface which reproduces the absorbed x ray intensity pattern. 10 The intrinsic spatial resolution characteristics of a-Se have been investigated previously. Que et al 11 used an analytic model to investigate seven different effects in a-Se.…”

“…18 Fundamental to image formation are the optical and dielectric anisotropies of individual LC molecules. 10 The dielectric anisotropy ͑⌬͒ defined as the difference in dielectric constants between the parallel direction, ʈ , and direction perpendicular to the long axis of the LC molecule, Ќ, causes the molecules to rotate and align their long axis with an applied electric field. The optical anisotropy, which depends on the orientation of the LC molecules, affects the propagation of light through the cell.…”

“…9 The use of an optical scanner and a reflective configuration has been proposed to reduce the size of the system and simplify readout. 10 By switching to a reflective LC cell, the light source and readout electronics can be confined to one side of the XLV. An optical scanner is used which mechanically scans a row of detector elements ͑dels͒, thus con-serving the pixel density of a static detector array, such as a CCD, while significantly reducing both the cost and bulk of the system.…”

“…The operation 10 of the XLV/scanner system to produce a digital radiograph involves three steps: Image formation, image digitization, and system reset. An overview of the operation of the XLV/scanner system is shown in Fig.…”